A laminated glass has excellent safety because a flying amount of broken pieces of glass is small if the laminated glass was broken by being subject to external impact. Therefore, the laminated glass is widely used for automobiles, railway cars, aircraft, ships, and architectural structures and the like. The laminated glass is manufactured by sandwiching an interlayer film between a pair of glass plates.
In recent years, reduction in the thickness of the laminated glass has been studied in order to reduce the weight of the laminated glass. When the thickness of the laminated glass is reduced, however, a sound insulation property is deteriorated. When the laminated glass having a low sound insulation property is used for a windshield of an automobile and the like, a problem that a sufficient sound insulation property for sound in a sound range of about 5000 Hz such as wind noise and driving noise of wipers cannot be obtained arises.
Consequently, improvement of the sound insulation property of the laminated glass by modifying materials of the interlayer film has been studied.
As one example of the interlayer film for laminated glass, Patent Document 1 discloses a sound insulation layer including 100 parts by weight of a polyvinyl acetal resin having an acetalization degree of 60 to 85 mol %, 0.001 to 1.0 parts by weight of at least one metal salt of alkaline metal salts and alkaline earth metal salts, and 30% by weight or more of a plasticizer. The sound insulation layer is used as a single layer interlayer film or a multi-layer interlayer film formed by laminating with other layers.